Here's another data point to expand on your thoughts below: I have a YH rim with K 1 9 5 20 YH on the outside at the valve stem hole, but on the inside it shows a '4' for the month. (see photos):

I would theorize that the 'inner' stamping is done after K-H makes/tests the rim, and then when the center is welded in, and the finished wheel meets test specs, they stamp the completed code next to the valve stem. In the case I show here, the rim is apparently made in April of 69, but the wheel isn't *finished* until May 20.. 3 weeks or more later (which seems long but.. there may have been reasons for that at times?). Does anyone actually know and can confirm any of the above conjecture?PS. Oh, and my 09C car, came with all YH rims marked as 5-20... which would be nearly 4 months between.

Now, as I am searching around for info, in prior years of 1969... KH rims being manufactured for Chevrolet, in my image above,the earlier rims only used a single J after the rim stamping of the size and width.Example : 14 X 5 JDoes the single J denote anything towards how the rim fits the brake system?Where as, in 1969 JJ stamping, does the JJ represent anything towards brake system fitment?

What is curious to me is if the early 1969 Z28 AD rims were stamped with JJ or J ?I would assume the the YH rims were having the JJ satmping.

In my image above, you will notice the letter A below the 14 of the 14X7 JJ stampings.I am going to guess that this denotes the month that it was made.This image is from one of my YJ rims in a set from January 1969.To add, there is also a letter in the wheel center that seems to denote the month of manufacture, K-1-9 A.On this particular rim, the A is stamped just under the GM stamp on the wheel center.I am going to assume that the outer band was manufatured in Jaunary, 1969 by looking at this.I am going to assume that the wheel center was manufatured in Jaunary, 1969 as well.

I decided to go and look at some of my other rims.K-1-8 trhru K-1-9 issue.Some of the K-1-8 rims have the Letter code in the wheel center on another of one of the 5 landings of the rim where it it can be stamped.One set, stamped for October, 1968 denotes a 10-X date.These rims show a K-1-8 with a Letter J.Counting out the months, J lands on the month of October.Thoughts....

My guess is is that both plants saw a drop off on manufacturing during the holidays. They were still producing but at a slower pace.

Once everyone was back to work, I would assume that production times and dates came back together.

Nope. The "pace" never changed - both plants ran at full linespeed all the time; there was no such thing as changing the linespeed without shutting the plant down and re-manning/re-training and re-tooling every operation in the plant. The line moved at 57 per hour at Norwood and 35 per hour at Van Nuys, every day, and they didn't have ten days off between Christmas and New Year's like they do today; they had Christmas Eve and Christmas day off, and New Year's Eve and New Year's day off.

Well, I had some of my extra YJ rims chem stripped and this process really cleans up the visibilty of the the codes on the rim bands.However, month and date codes are not consistent as it seems when they were at KH being date stamped.Letters and numbers can be found, and can be random.I think either is correct.Checking date codes at the valve stems, codes in the center of the rim, to codes in the band will help somewhat in ID'ing these.Here are a few pics from a set I am selling :

The following pic is of a Oct.68 "AD" rim. I don't believe the "A" is the month. Under the "JJ" is a "10". I believe that is the month. It would be nice to see you include the "AD" rim in your research.

Do you have a pic of the date codes near the valve stem hole? I'd like to compare to mine. Thanks.